摘要:

The dependence of time to ignitionti, on heightxof a specimen is examined for radiant ignition of vertical cellulosic solids. There is a transitional irradiance value of about 4 cal/cm2sec, below whichti, decreases asXincreases and above whichti, is essentially independent ofX. In the present paper this phenomenon is explained on the basis of the time ts, required for establishment of a steady-state free-convection boundary layer. At low irradiance,ti, ≥tss, andx-dependent heat losses through the boundary layer cause the top of the panel to be hotter than the bottom and cause the pyrolysis rate and ignition time to depend onX. At high irradiance,ti, ≤tss, and ignition occurs before boundary-layer development, thereby causingti, to be independent ofX.

ISSN:0010-2202    

DOI:10.1080/00102206908952220

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

Reflected shock waves have been used to heat argon-diluted mixtures of nitrous oxide with cyanogen or hydrogen cyanide to temperatures between 1500 and 2000 °K. The NCN radical has been detected spectroscopically in both systems during the induction period to explosion. Results for the temperature dependence of the ignition delay suggest that nitrous oxide decomposition is rate controlling for C2N,-N2O mixtures whereas the reactions

ISSN:0010-2202    

DOI:10.1080/00102206908952221

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

The structure of a steady one-dimensional isobaric deflagration is examined for the case of a direct first-order one-step irreversible exothermic unimolecular decomposition under Arrhenius kinetics. In particular, the eigenvalue giving the speed of propagation of the laminar flame into the unburned gas is sought for constant Lewis number of order unity. The method of matched asymptotic expansion is invoked in the physically interesting limit of activation temperature large relative to the adiabatic flame temperature. The leading approximation for the eigenvalue is found to be a generalization of the result given by Zeldovich, Frank-Kamenetski, and Semenov for Lewis number unity. The first two terms in the asymptotic expansion for the eigenvalue yield an expression superior to any previously published.

ISSN:0010-2202    

DOI:10.1080/00102206908952222

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

Experimental observations are presented on flame propagation along uniform, linear, horizontal arrays of vertically oriented matchsticks. Matchstick height and spacing between matchsticks are varied. Reported results include necessary conditions for flame propagation, linear rates of flame propagation, and char angle—the angle between the horizontal and a photographically recorded line of incipient char formation on the face of the matchstick array. Theoretical explanations for the experimental observations are offered on the basis of a model which employs an ignition temperature and uses previously determined flame shapes for individually burning cellulosic cylinders. The remarkably good agreement between theory and experiment supports the contention that convective effects are of primary importance in flame propagation at matchstick size scales.

ISSN:0010-2202    

DOI:10.1080/00102206908952223

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

High ignition temperatures for Al and Be are responsible in part for inability of additives of these metals to attain theoretical performance in propulsion systems. A model of metal ignition has been developed which suggests that more efficient ignition of these metals will be observed if they are coated with films of Mg or Ca [Mellor and Glassman (1965), (1969), and Mellor (1967)], In the present paper experimental verification of the improvement in ignition for Al wires coated with thin films of Mg or Ca is discussed. Several pretreatments of the Al wires were used; in some, the room-temperature film of Al203was removed. The best results were obtained if the natural A1203film was removed by an amalgamation pretreatment and the clean Al surface which resulted was coated with Mg. It is thought that similar techniques will improve the ignition efficiency for Be.

ISSN:0010-2202    

DOI:10.1080/00102206908952224

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

The classical wave-model for the laminar, adiabatic combustion of a homogeneous, pre-mixed, gaseous flame is expanded and applied to the heterogeneous combustion of a pure solid propellant. The conservation equations for the gas, solid and Gibbsian surface states are solved to obtain an explicit expression for the steady-slate burning rate. The major problem of predicting the magnitude of the gas-phase heating rate, is resolved by relating the heating rate to the burning velocity of a simulated flame above the solid surface. The theory is readily modified to include energy loss corrections for the non-adiabatic processes of conduction, convection and radiation to the surroundings. The theory predicts a magnitude for the burning rate of pure ammonium perchlorate that is in good agreement with experiment

ISSN:0010-2202    

DOI:10.1080/00102206908952225

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

An analytical study has been made of the kinetics of formation of NO in hydrocarbon-air combustion. Two UNIVAC 1108 computer programs were utilized to obtain time-dependent concentrations of chemical species in a subsonic stream. Inlet conditions specified were the temperature, pressure, and composition. Inlet tempera-lures were varied from 1000 K to 2000 K at pressures of 1 to 10 atm for equivalence ratios of 0.8 to 1.25. The inlet composition was taken lo be a mixture of non-reacted gases. It was found that equilibrium in the nitrogen oxides is very slowly attained with respect to the carbon and hydrogen oxides. The implication of this result is that observations of NO concentrations well below equilibrium values in certain types of engine exhausts may be correlated with the kinetics of formation, and that combustion temperatures and residence times, rather than exhaust temperatures, determine the level of NO in exhaust gases.

ISSN:0010-2202    

DOI:10.1080/00102206908952226

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

This investigation relates to the study of reactions between liquid and solid phases. This report describes the study of the influence of pressure on the rate of ablation of solid urea by liquid nitric acid in the range of 1-30 bars. The experimental results obtained are first given, followed by an attempt at interpretation by introducing a relation between pressure and the temperature at the reaction interface and by postulating the existence of an adsorbed layer on the surface of the solid. Three distinct ablation patterns have been uncovered, one at low flow rates where the ablation rate is independent of pressure and is a function of flow only; one at high flow rates where the ablation rate is independent of flow, is a function of pressure only and becomes constant at high pressures; and an intermediate pattern where the ablation rate is a function both of flow and pressure. The results obtained are exactly analogous to those noted in gas-solid ablation, which makes it possible to extend the theoretical interpretation to these phenomena.

ISSN:0010-2202    

DOI:10.1080/00102206908952227

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

A theoretical study of the problem of ignition of a cold combustible mixture by a hot projectile is performed by approximating, firstly, the flow over its surface to a laminar flow of the mixture over a hot plate, and, secondly, the flow in the wake of the projectile to a plane laminar mixing of the cold unreacted mixture with the hot combustion products. Unlike the earlier analyses consisting of successive approximations and/or series expansions, the non-similar boundary layer equations are directly integrated by following a suitable numerical scheme. A characteristic parameter of the problem—the distance at which ignition occurs, which is defined by the presence of a temperature maximum—is obtained for different values of quantities relating to the properties of propane-air mixture, and to the speed as well as the dimensions of the projectile.

ISSN:0010-2202    

DOI:10.1080/00102206908952228

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor